Lower Limpopo near its mouth at flood stage in the noted floods of year 2000. Source: NASA

The Limpopo River is one of the great rivers of southern Africa, with a catchmentCatchment is the entire area of a hydrological drainage basin. basin of approximately 410,000 square kilometers. The human population in the Limpopo Basin is approximately fifteen million, with a greater concentration in the lowlands of the downriver portion of the basin; the majority of the basin population is considered to be living in poverty, with the catchment generally overpopulated with respect to land that can be supplied by water for farming.

Topography of the Limpopo River basin. Source: Food and Agricultural Organization (FAO), 2005

The Waterberg Massif and Soutpansberg Mountains are the highest topographic features in the basin, although the larger portion of the catchment is a low lying eastern coastal plain comprising approximately two thirds of the land area of the basin. The majority of the Limpopo Basin incurs less than 40 centimeters of rainfall per annum, with the preponderance of precipitation occurring between October and April; most of the basin is classified as arid or semi-arid.

Hydrology

At its point of discharge to the Indian Ocean within Mozambique, the mean flow rate of the Limpopo is 170 cubic meters per second. Flow of the Limpopo is generally languid, and the river carries a heavy silt load. The LimpopoheadwatersHeadwaters are the source of water at the origin of a river or stream. are considered to arise at the confluence of the Marico River and the Crocodile River within South Africa's Limpopo Province; thence the Limpopo flows north to create a portion of the border with Botswana where it arcs eastwardly, to be joined with flow from the Shashe River, establishing the border with Zimbabwe. Thereafter, the Limpopo proceeds down the Great Escarpment eastward into Mozambique at Pafuri, and finally flows across a coastal plateau to the Indian Ocean at Xai Xai.

In the upper reaches within South Africa and Botswana, the Marico, Crocodile and Mogalakwena Rivers are the largest influent sources. In the middle reaches of eastern Botswana, southeastern South Africa and Zimbabwe, the chief tributaries are the Shashe, the Umzingwane and the Sand Rivers. In the lower reaches, major inflows are from the Mwenezi, Changane and Elephants Rivers. Significant periodic flooding occurs along the lower reaches of the Limpopo in Mozambique, during the rainy season.

Water quality

Elevated nitrate levels are found in portions of the Limpopo Basin, most notably in elements of the groundwater basins. For example aquifers in the Bochum Province of South Africa have been analyzed, with the results of high nitrate and elevated organic carbon. One hypothesis is that injection of untreated sewage to the aquifer accounts for both phenomena.
African elephants at the Sand River, a Limpopo tributary. @ C.Michael Hogan

The Changane catchment has been shown to be significantly polluted due to point source discharges leading low dissolved oxygen and high total dissolved solids, electric conductivity, total hardness, sodium adsorption ratio and low benthic macroinvertebrates taxa. At the most upstream elements of the Mozambique reaches of the Limpopo The water quality monitoring data indicates that sites located at proximities to the border with upstream countries are contaminated with heavy metals.

Water quality issues are exacerbated by the periodic droughts, but also from over-extraction of rivers in the Limpopo Basin, due to overpopulation and over-intensive farming relative to available basin water resources. For example, abstraction of surface water in the Luvuvhu River, a tributary of the Limpopo, in the Kruger Reserve, has led to diminished water qualtiy, and in some cases virtual cessation of flow and severe adverse impacts to aquatic and riparian biota.

Aquatic biota

Redbreast tilapia, native to the Limpopo. @ Frederick Hermanus Van der Bank
Some of the largest native demersal vertebratefishes of the Limpopo River system include the 117 centimeter (cm) long tiger fish (Hydrocynus vittatus) and the 175 cm African mottled eel (Anguilla bengalensis labiata), the 35 cm snake catfish (Clarias theodorae) and the 32 cm bulldog (Marcusenius macrolepidotus). Demersal river fish are found at the river bottom, feeding on benthos and/or zooplankton.

Alien species that have been introduced into the Limpopo Basin include the following fishes: Oreochromis niloticus, Oreochromis machrochir, Cyprinus carpio, Micropteris salmoides and M. dolomica.

Terrestrial ecoregions

The ecoregions within the Limpopo catchment span portions of the countries of Botswana, South Africa, Zimbabwe and Mozambique. Special ecosystems within the basin include pans and vleis. A pan is a depression in the local topography, where rainwater collects and typically evaporates prior to discharge to a surface channel. A vlei is a location where the water table is high, and ephemeral or permanent wetlands may exist. Most of the Limpopo Basin wetlands are in the lower reaches of the river along the Mozambique floodplains.

The Maputaland coastal forest mosaic exhibits high faunal diversity and endemism. More than 470 bird species are found here and four species and 43 subspecies endemic or near endemic. The endemic Neergaard’s sunbird (Nectarinia neergaardi) is particularly interesting, as it is restricted almost entirely to the dry semi-deciduous sand forest of Maputaland. Rudd’s apalis (Apalis ruddi) is also near endemic, together with the pink-throated twinspot (Hypargos margaritatus), and the lemon-breasted seedeater (Serinus citrinipectus).

Prehistory

The Limpopo Basin is an important locus for early hominids, particularly in the portion of the basin in northern South Africa, including the Waterberg Massif. Considerable rainfall (in earlier ages) and the ability of sandstone to retain ample aquifers provided a hospitable habitat for early man. The table rock formations and cliff overhangs offered natural shelters and even caves for these early peoples. The first human ancestors probably inhabited the Waterberg Massif as early as three million years ago, since Makapansgat, only 40 kilometers to the east has yielded skeletons of Australopicthecus africanus dating above three million years. Homo erectus remains dating to one million years were also discovered in Makapansgat. A. Africanus, subsisting on plants and invertebrates, probably lived on valley floors; however, H. Erectus, a hunter, may have purposefully moved into the higher areas of the Waterberg for summer (December to March) game. At the periphery of the Waterberg in Olieboomsport later Acheulian artifacts were found, indicative of the early stone age. The earliest hard evidence of man in the heart of Waterberg (at Goudriver) is from the Middle Stone Age, where stone tools in cave shelters have been dated at 200,000 to 30,000 BC.

Bushmen from the Botswana region migrated south to the Waterberg around the time of Christ. They left rock paintings at Lapala and Goudriver recording their life and times, including characterizations of rhinoceros, elephant and a variety of antelope species (resembling impala, kudu and eland, all present day inhabitants). Early Iron Age settlers in Waterberg by 450 AD were the Bantu, an advanced tribe skilled in metal-working and cattle herding. The Bantu migrated from Nigeria, but their arrival with cattle created an environmental disaster in the lower plains around Waterberg, since cattle grazing decreased grasses in favour of increasing certain brush species conducive to reproduction of the tse-tse fly. The resulting epidemic of sleeping sickness depopulated the human settlements on the plains, but life on the Waterberg Massif itself thrived, since the fly cannot tolerate altitudes exceeding 600 meters.

References

M.Chilundoa, P.Keldermanb, J.H.O´keeffe. 2008. Integrated Water Resources Management: From Concept to Practice. Design of a water quality monitoring network for the Limpopo River Basin in Mozambique. Physics and Chemistry of the Earth, Parts A/B/C. Volume 33, Issues 8–13, Pages 655–665